The prior art of motor-powered depilatory devices for removing skin hair is based on a well-known concept disclosed in a patent covering an earlier mechanical device, namely Swiss Patent 268,696 to Fischer. There, a helical spring is arched to provide spaces between loops of its convex side, and the spring is placed on the skin under slight pressure and rolled in the direction of hair growth. The rolling motion of the helical spring causes hairs which become trapped in the spaces between the coil loops on the convex side to be plucked when these spaces close on the coil spring concave side.
U.S. Pat. No. 4,524,772 to Daar, et. al., discloses an arched helical spring which is provided with high speed rotational motion via motor-driven couplings connected at its ends. As with the helical spring in the mechanical design of Fischer, the power-driven helical spring grabs individual hairs when the spaces between its loops close. Upon detailed inspection it is seen that the contact between the helical spring wire and individual hairs is essentially point-like. In some cases, rather than being plucked and removed, the hair is instead torn or cut at a weak point thereon, leaving hair "stubble" on the skin.
Once a hair becomes trapped between closed helical spring loops, continued application of rotational force causes the spring to "wind up" since it is composed of flexible wire material, yet the hair is still in place. As the spring continues to "wind", the pulling tension applied to the hair increases until the necessary force is developed for plucking. Because a finite interval is required for this force to be developed, the user is subjected to an increased pain level. This problem has been identified in connection with the commercial model of the device sold under this patent.
As with other metal objects continually subjected to bending stresses, or due to manufacturing defects, the helical spring may break during use, creating a hazard of puncturing and penetrating the skin over which it passes. Another disadvantage to this design is the transverse deflection of hair due to lateral movement of the spaces between the helical spring loops which rotate in spiral fashion. This tends to limit the degree of certainty that hairs will be plucked, as shorter hairs will not remain within a given loop as it moves laterally.
In U.S. Pat. No. 4,726,375 to Gross, et. al., a motor-powered depilatory device is disclosed which employs a hair-plucker body comprising a plastic or rubber cylindrical member having a smooth outer surface formed with a plurality of partially circumferential slits. The cylindrical member is rotatable about its longitudinal axis and is supported in an arcuate position such that the slits open and close during rotation, trapping and plucking hairs therein. Because they are only partially circumferential, the slits are effective only during a portion of the rotation, reducing overall efficiency.
By use of the soft plastic or rubber material, a greater contact area is afforded the individual hairs which are trapped within the slits of the cylindrical element. While this represents an important departure from the helical spring plucking operation, the soft plastic or rubber material also exhibits the "winding" phenomenon because of its flexibility. Thus, this design is also subject to increasing the pain associated with plucking of individual hairs.
In addition, since the material is soft and has a high friction coefficient, friction with the skin is increased, requiring an increased motor rating for maintaining a given rotational speed. Also, the partially circumferential slits in the plucker body constitute weak points, causing it to "tear" apart and limiting its durability.
In U.S. Pat. No. 4,807,624 to Gross et al, there is disclosed an alternative embodiment to that of the '375 patent to Gross et al. Here, the hair-plucker body comprises a stack of circular discs of uniform diameter fixed to a resilient cylindrical core of smaller diameter passing through their centers. Since the core is resilient, it is subjected to torsion forces and tends to "wind" as the discs develop sufficient hair pulling tension for plucking. In time, the core develops weak points as it carries both tensioning and torsional forces.
In U.S. Pat. No. 4,575,902 to Alazet, there is disclosed a depilatory device comprising a series of adjacent, closely-spaced hair-plucking discs driven by an electric motor housed within a casing. The discs are periodically deformed during their rotation, such that adjacent ones thereof are pressed together to pluck hairs which may have become trapped between them when the unit is passed over the skin. Besides its mechanical complexity, a drawback to this design is associated with the fact that the discs close only periodically, making the plucking action inefficient by limiting it to a short time interval.
U.S. Pat. No. 2,900,661 to Schnell discloses a plucking device for feathers, hairs or the like in which at least one pair of discs rotate at an angle to each other and converge at one contact point whereat hairs are plucked. The disadvantage associated with this design stems from the large spacing between disc pairs, which reduces efficiency, in addition to being expensive and complicated.
Therefore, it would be desirable to provide a power-driven depilatory device which provides efficient hair removal and reduces hair stubble, while minimizing pain associated with the interval between grasping and plucking of individual skin hairs.
It would also be desirable to provide a depilatory device which is simple in construction for cost-effective production, while durable in use.
Additionally, it would be desirable to provide a depilatory device which minimizes heat and friction when in contact with skin, while also eliminating helical spring breakage hazards near the skin.